The invention relates to a method of producing discontinuous fibers from a thermoplastic material having a high melting point (i.e. glass), and more particularly to fiber production utilizing a sizing agent specifically designed for non-continuous fibers.
In the prior art, non-continuous fibers are combined with one another to form hybrid threads or rovings, which can be manufactured at less expense than traditional continuous fibers and can be used in the composition of numerous products employed in widely diverse applications. For example, it is known to produce hybrid threads from glass fibers used to manufacture protective clothing, sealing gaskets or filter cloths because of its particularly advantageous physical and chemical properties.
Methods of the prior art include forming continuous thread fibers by forcing molten glass under centrifugal force through a number of orifices in a hollow rotating body to form thin streams of molten glass. The thin streams are mechanically drawn, and produce a large number of continuous glass filaments which are then attenuated and glued together to form a continuous thread.
French Patent 2,497,239 discloses a method for producing hybrid threads of glass and support fibers, wherein continuous glass threads are cut to lengths ranging from 10 to 100 millimeters. U.S. Pat. No. 2,706,377 discloses a method for cutting continuous threads as long as 1000 millimeters which are utilized to form hybrid threads. Cut threads can be used for varying applications depending on the characteristics of the thread, such as the diameter and length of the individual filaments.
In all continuous fiber forming operations, sizing of filaments is necessary to reduce possible damage to the resultant fiber. Sizing is a process of coating the fibers or filaments with a sizing agent to protect the surface of the filaments and the resultant thread from abrasion. Without this protection, glass fibers produced may become damaged during the various required handling operations. Sizing also ensures cohesion of the filaments, thereby acting as a gluing agent and ensuring the proper formation of the threads, while eliminating the gluing process. Depending upon the desired application, sizing is used to impart necessary properties to the thread (i.e., cohesiveness, lubrication, etc.), and can comprise largely varying ingredients. Typically, hybrid threads of the prior art have utilized conventional sizing agents such as "textile" or "plastic" sizes (usually used on continuous fibers). U.S. Pat. No. 4,584,110 describes a sizing agent specifically designed for use with cut fibers. However, this sizing agent is made of many more elements than conventional sizing agents and is therefore more difficult to produce.